bnf.txt

<statements> ::= { <statement> }

<statement> ::= "var" <ident> { “,” <ident> } “;”
				
			  | "let" <ident> “=“ <expression> “;”

			  | "if" <expression> <relop> <expression> “{”
					<statements> 
				“}”
				[ "else" "{"
					<statements>
				"}"]

		  	  | "while" <expression> <relop> <expression> “{”
					<statements>
				“}”

			  | "print" ( <expression> | <string> ) { "," ( <expression> | <string> ) } “;”

			  | "input" <ident> “;”


<expression> ::= [ + | - ] <term> { ( + | - ) <term> }

<term> ::= <factor> { ( * | / ) <factor> }

<factor> ::= <ident> | <constant> | "(" <expression> ")"

<ident> ::= <letter> { <letter> | <digit> }

<string> ::= "”" { <letter> | <digit> } "”"

<letter> ::= a | .. | Z

<constant> ::= <digit> { <digit> }

<digit> ::= 0 | .. | 9

<relop> ::= <[=] | >[=] | =